Centrosomes form the poles of the mitotic spindle and play a key role in the execution of most mitotic events. They are involved in determining the quantity and distribution of astral microtubules; chromosome alignment and movement; and cleavage furrow formation. Also, centrosomes show a specific pattern of replication at each cell cycle. Recent work shows that isolated basal bodies will form asters when injected into amphibian eggs. However, it is not known if these asters can function as centrosomes. If basal bodies are treated with RNAases before injection, they do not form asters. The work described in this proposal will use this sor of approach to: 1) further characterize the formation, function, reproduction of centrosomes, and 2) better define the role of centrosomal RNA in these processes. I will use sea urchin eggs for this work because they are optically clear, allowing me to observe centrosomal development and function in vivo. I will isolate sea urchin centrioles, established centrosomes, and monasters and then inject them into fertilized eggs at different points in the cell cycle. By characterizing and comparing the properties of the centrosomes formed by these isolates I can answer a number of questions on centrosome function. In addition, I will treat these isolates before injection with RNAases to remove RNA or with a psoralen to crosslink double stranded RNA. I will determine the ability of the centrosomes formed by such treated isolates to perform as normal centrosomes. The ability of these centrosomes to replicate is of particular interest. This work will provide a better understanding of the mechanisms of that control cell division in normal and cancerous cells.